Two-interval Discrimination Research Articles

The role of eye movements in perceiving vehicle speed and time-to-arrival at the roadside

To avoid collisions, pedestrians depend on their ability to perceive and interpret the visual motion of other road users. Eye movements influence motion perception, yet pedestrians’ gaze behavior has been little investigated. In the present study, we ask whether observers sample visual information differently when making two types of judgements based on the same virtual road-crossing scenario and to which extent spontaneous gaze behavior affects those judgements. Participants performed in succession a speed and a time-to-arrival two-interval discrimination task on the same simple traffic scenario—a car approaching at a constant speed (varying from 10 to 90 km/h) on a single-lane road. On average, observers were able to discriminate vehicle speeds of around 18 km/h and times-to-arrival of 0.7 s. In both tasks, observers placed their gaze closely towards the center of the vehicle’s front plane while pursuing the vehicle. Other areas of the visual scene were sampled infrequently. No differences were found in the average gaze behavior between the two tasks and a pattern classifier (Support Vector Machine), trained on trial-level gaze patterns, failed to reliably classify the task from the spontaneous eye movements it elicited. Saccadic gaze behavior could predict time-to-arrival discrimination performance, demonstrating the relevance of gaze behavior for perceptual sensitivity in road-crossing.

Discrimination of interaural intensity differences and monaural intensity increments

This study assessed the equivalence of a binaural task (two-interval discrimination of interaural intensity differences, IIDs) and a monaural two-interval increment-discrimination task, in which each interval consisted of two noise bursts of different intensities, with listeners identifying the interval with the larger intensity change. Stimuli were broadband noise, with trial-by-trial feedback provided. An overall level rove between intervals forced listeners to compare the two signals within each interval (across ears in the binaural task and across bursts in the monaural task). Both tasks involved presentation of four signals of different intensities, yielding the same optimal decision statistic. Assuming (1) discrimination of IIDs across intervals amounts to discrimination of lateral position and (2) variability in lateral position increases with IID leads to a prediction of Weber's law. Functions relating threshold IID delta (or monaural increment delta) in dB to the standard IID (or increment) in dB had nearly equal slopes in binaural (0.054) and monaural (0.058) conditions. While the derived binaural decision statistic is based on discrimination of an emergent percept of the stimulus (intracranial position), the similarity of results suggests that monaural increment-discrimination may be based on discrimination of a similarly emergent percept (a loudness step). [Work supported by NIH R01DC00683.]

Haptic two-dimensional angle categorization and discrimination

This study examined the extent to which haptic perception of two-dimensional (2-D) shape is modified by the design of the perceptual task (single-interval categorization vs. two-interval discrimination), the orientation of the angles in space (oblique vs. horizontal), and the exploration strategy (one or two passes over the angle). Subjects (n = 12) explored 2-D angles using the index finger of the outstretched arm. In the categorization task, subjects scanned individual angles, categorizing each as "large" or "small" (2 angles presented in each block of trials; range 80° vs. 100° to 89° vs. 91°; implicit standard 90°). In the discrimination task, a pair of angles was scanned (standard 90°; comparison 91-103°) and subjects identified the larger angle. The threshold for 2-D angle categorization was significantly lower than for 2-D angle discrimination, 4° versus 7.2°. Performance in the categorization task did not vary with either the orientation of the angles (horizontal vs. oblique, 3.9° vs. 4°) or the number of passes over the angle (1 vs. 2 passes, 3.9° vs. 4°). We suggest that the lower threshold with angle categorization likely reflects the reduced cognitive demands of this task. We found no evidence for a haptic oblique effect (higher threshold with oblique angles), likely reflecting the presence of an explicit external frame of reference formed by the intersection of the two bars forming the 2-D angles. Although one-interval haptic categorization is a more sensitive method for assessing 2-D haptic angle perception, perceptual invariances for exploratory strategy and angle orientation were, nevertheless, task-independent.

Target Detection by Opponent Coding in Monkey Prefrontal Cortex

The pFC plays a key role in flexible, context-specific decision making. One proposal [Machens, C. K., Romo, R., & Brody, C. D. Flexible control of mutual inhibition: A neural model of two-interval discrimination. Science, 307, 1121-1124, 2005] is that prefrontal cells may be dynamically organized into opponent coding circuits, with competitive groups of cells coding opposite behavioral decisions. Here, we show evidence for extensive, temporally evolving opponent organization in the monkey pFC during a cued target detection task. More than a half of all randomly selected cells discriminated stimulus category in this task. The largest set showed target-positive activity, with the strongest responses to the current target, intermediate activity for a nontarget that was a target on other trials, and lowest activity for nontargets never associated with the target category. Second most frequent was a reverse, antitarget pattern. In the ventrolateral frontal cortex, opponent organization was strongly established in phasic responses at stimulus onset; later, such activity was widely spread across dorsolateral and ventrolateral sites. Task-specific organization into opponent cell groups may be a general feature of prefrontal decision making.

From memory-based decisions to decision-based movements: A model of interval discrimination followed by action selection

The interval discrimination task is a classical experimental paradigm that is employed to study working memory and decision making and typically involves four phases. First, the subject receives a stimulus, then holds it in the working memory, then makes a decision by comparing it with another stimulus and finally acts on this decision, usually by pressing one of the two buttons corresponding to the binary decision. This article demonstrates that simple linear readouts from generic neural microcircuits that send feedback of their activity to the circuit, can be trained using identical learning mechanisms to perform quite separate tasks of decision making and generation of subsequent motor commands. In this sense, the neurocomputational algorithm presented here is able to integrate the four computational stages into a single unified framework. The algorithm is tested using two-interval discrimination and delayed-match-to-sample experimental paradigms as benchmarks.

Flexible Control of Mutual Inhibition: A Neural Model of Two-Interval Discrimination

Networks adapt to environmental demands by switching between distinct dynamical behaviors. The activity of frontal-lobe neurons during two-interval discrimination tasks is an example of these adaptable dynamics. Subjects first perceive a stimulus, then hold it in working memory, and finally make a decision by comparing it with a second stimulus. We present a simple mutual-inhibition network model that captures all three task phases within a single framework. The model integrates both working memory and decision making because its dynamical properties are easily controlled without changing its connectivity. Mutual inhibition between nonlinear units is a useful design motif for networks that must display multiple behaviors.

Spectral-shape discrimination. I. Results from normal-hearing listeners for stationary broadband noises.

This research is concerned with the ability of normal-hearing listeners to discriminate broadband signals on the basis of spectral shape. The signals were six broadband noises whose spectral shapes were modeled after the spectra of unvoiced fricative and plosive consonants. The difficulty of the discriminations was controlled by the addition of noise filtered to match the long-term speech spectrum. Two-interval discrimination measurements were made in which loudness cues were eliminated by randomizing (roving) the overall stimulus level between presentation intervals. Experimental results, examined as a function of intensity rove width, stimulus duration, and stimulus pair, were related to the predictions of a simple filter-bank model whose fitting parameter provides an estimate of internal noise. Most results, with the notable exception of duration effects, were predicted by the model. Estimates of internal noise in each frequency channel averaged roughly 7 dB for long-duration stimuli and 13 dB for short-duration stimuli. Results and predictions are compared to results of other studies concerned with the discrimination of spectral shape.